Considerations, evaluations, investigations and searching

ABSTRACT

Methods of considering DNA based links between two or more situations are provided. Amongst the methods is a method including obtaining a plurality of test results, each test result relating to a situation, each test result including information on the DNA from that situation, the plurality of test results providing a group of test results; selecting a plurality of test results from the group of test results, the plurality of results for the combination of test results; considering a genotype as possibly giving rise to each of the test results of the combination, evaluating the support for that genotype giving rise to all of the test results of the combination; considering the genotype as a DNA based link between the situations for the test results in a combination if the support meets the defined criteria. The methods provide new techniques for considering preexisting DNA test results and/or new DNA test results so as to establish links between them in terms of the genotypes which are supported as contributing to them. The methods enable the evaluation of the support for genotypes given the test results in relation to various combinations of test results.

This invention concerns improvements in and relating to considerations,evaluations and investigations, particularly but not exclusively inrelation to highlighting genotypes of interest, and to searching,particularly but not exclusively in relation to searching of databasesof genotypes.

Substantial numbers of DNA test results exist from various scenes,samples taken from scenes and replicates of samples. These relate toboth solved and unsolved incidents. It is desirable to be able to obtainas much information as possible from the consideration or evaluation ofthese test results. The present invention seeks to provide asignificantly more powerful tool for this purpose than presently exists.

A substantial number of genotypes are also recorded, for instance in TheNational DNA Database (UK Registered Trade Mark) of genotypes in the UK,and these provide a potential source of information to be considered.The present invention seeks to provide a significantly more powerfultool for considering the information in such databases.

The present invention has amongst its aims to provide new techniqueswhich enable useful information to be obtained by consideringpre-existing DNA test results alone or in combination with new DNA testresults so as to establish links between some of those test results interms of genotypes which are supported as contributing to them. Thepresent invention has amongst its aims to evaluate the more supportedgenotypes given the test results in relation to various combinations oftest results.

According to a first aspect of the invention we provide a method ofconsidering DNA based links between two or more situations, the methodincluding:

-   -   obtaining a plurality of test results, each test result relating        to a situation, each test result including information on the        DNA from that situation, the plurality of test results providing        a group of test results;    -   selecting a plurality of test results from the group of test        results, the plurality of results forming a combination of test        results;    -   considering a genotype as possibly giving rise to each of the        test results of the combination, evaluating the support for that        genotype giving rise to all of the test results of the        combination;    -   considering the genotype as a DNA based link between the        situations for the test results in the combination if the        support meets defined criteria.

According to a second aspect of the invention we provide a method ofconsidering DNA based links between two or more situations, the methodincluding:

-   -   obtaining a plurality of test results, each test result relating        to a situation, each test result including information on the        DNA from that situation, the plurality of test results providing        a group of test results;    -   selecting a plurality of test results from the group of test        results, the plurality of results forming a combination of test        results;    -   considering a genotype as possibly giving rise to each of the        test results of the combination, evaluating the support for that        genotype giving rise to all of the test result of the        combination;    -   considering the genotype as a DNA based link between the        situations for the test results in the combination if the        support meets defined criteria;    -   comparing a genotype which is considered a DNA based link        against records of genotypes to identify matching genotypes in        the records.

The second and/or third aspects of the invention may include any of thefeatures, options or possibilities set out elsewhere in this document,including the third and fourth aspects of the invention.

The situations may be test results for different scenes and/or differentsamples from the same or different scenes and/or replicates from thesame samples or from different samples. The situations may include testresults for one or more known individuals. The test results may relateto mixtures and/or single contributor cases. The test results may relateto complete and/or partial profiles.

The information on the DNA may be the allele present at a loci, ideallyfor at least 6 different loci. The information may include the peakheight and/or peak area for those alleles. Complete or partial profilesmay be accepted as test results for application of the method.

The group of test results may be stored as a group or may be pulledtogether from discrete sources. The discrete sources may be pulledtogether to form a group. Alternatively one or more test results fromsuch sources may be pulled together to form a group for the purposes ofthe application of the method.

All possible combinations of test results for the test results in thegroup may be considered. Pairs, triplets and quadruplets of test resultsmay particularly be considered.

The evaluation a direct evaluation of the support for a genotype givingthe combination of test results or may involve an evaluation of thesupport for a given genotype giving each of the test results, theindividual evaluations being combined to give the overall evaluation.

The support may meet the defined criteria when the probability that thegenotype could have given rise to the test results of the combination isabove a given level. The level may be predetermined.

The support may meet the defined criteria when an expression of thesupport that the genotype could have given rise to the test results ofthe combination is below a given level. That level may be predetermined.

The method may be used to establish DNA based links between differentscenes. The method may be used to establish DNA based links betweendifferent samples taken from different parts of the same scene. Themethod may be used to establish DNA based links between replicates ofthe same sample. The method may be used to establish DNA based linksbetween combinations of such situations. The method may be used toestablish a DNA based link between a person whose genotype is known andone or more situations.

The method may be used to establish DNA based links between test resultswhich are ambiguous or which could be suggested to be ambiguous. Suchtest results might be one or more of test results which are or could bemixtures and/or test results which are or could involve low levels ofDNA in the sample for one or more persons (low levels could be though ofas less than 500 pg or even less than 100 pg of DNA) and/or test resultswhich do or could involve effects due to stutter and/or allele drop outand/or allele contamination and/or preferential amplification.

The method may be used to establish a genotype or genotypes which areDNA based links between situations and which are then matched to anexisting genotype record, ideally for a known person.

According to a third aspect of the invention we provide a method ofconsidering DNA based links between two or more situations, the methodincluding:

-   -   obtaining a plurality of test results, each test result relating        to a situation, the test results including information on the        DNA from the corresponding situation, the plurality of test        results providing a group of test results;    -   selecting a combination of test results which includes a        plurality of test results from the group of test results;    -   considering one or more genotypes as possibly giving rise to the        combination of test results and evaluating for each of those        genotypes the support that the genotype gave rise to the        combination of test results;    -   considering a genotype whose support meets defined criteria as a        DNA based link between the situations of the combination.

The third aspect of the invention may include any of the features,options or possibilities set out in this document, but particularly fromamongst the following.

Preferably the evaluation of the support for a genotype giving rise tothe combination of test results includes a consideration of theprobability of the test results arising given that genotype and theprobability of occurrence of that genotype. Preferably the evaluation ofthe support for the genotype giving rise to the combination of testresults includes a consideration of the overall probability of the testresults arising given that genotype and the probability of occurrence ofthat genotype, for all possible genotypes. Preferably the evaluation ofthe support for a genotype giving rise to the combination of testresults includes a consideration of the probability of the test resultsarising given that genotype and the probability of occurrence of thatgenotype against a consideration of the overall probability of the testresults arising given that genotype and the probability of occurrence ofthat genotype, for all possible genotypes.

Preferably the evaluation of the support for a genotype giving rise tothe combination of test results is defined by${\Pr\left( G_{l} \middle| {D\ldots} \right)} = {\frac{\prod\limits_{ijk}\quad{{\Pr\left( D_{ijk} \middle| G_{l} \right)}{\Pr\left( G_{l} \right)}}}{\sum\limits_{i}\quad{\prod\limits_{ijk}\quad{{\Pr\left( D_{ijk} \middle| G_{l} \right)}{\Pr\left( G_{l} \right)}}}}{for}\quad{all}\quad{l.}}$where G₁ represents the particular genotype, D represents thecombination of test results, potentially including test results due tovarious scenes and/or samples from scenes and/or replicates of samplesfrom scenes, i represents the range of replicates, j the range ofsamples, k the range of scenes and l the range of genotypes underconsideration.

Preferably the method is applied to a plurality of combinations selectedfrom the group of test results. Each possible combination of testresults from amongst the group of test results may be considered.Combinations may include two, three, four or more test results from thegroup. A combination may include one or more test results for asituation which is from a different scene to one or more othersituations represented by test results in the group. A combination mayinclude one or more test results for a situation which is from adifferent sample to one or more other situations represented by testresults in the group. A combination may include one or more test resultsfor a situation which is from a different replicate to one or more othersituations represented by test results in the group.

Each possible genotype may be considered as giving rise to thecombination of test results. One or more limits may be applied to thegenotypes which are considered from amongst the full set of possiblegenotypes. The limits may be based on one or more rules as to genotypeswhich could not practically give one or more of the results in thecombination being considered.

The evaluation may be expressed as a posterior probability.

Preferably the evaluation of the support for a genotype giving rise tothe group of test results includes a consideration of the effect of oneor more of contamination of the test results and/or allele drop out fromthe results and/or stutter in the results and/or preferentialamplification of the results.

The method may be used to consider one or more test results which aremixtures. The method may be used to consider one or more test resultswhich contain low levels of DNA from one or more persons. The method maybe used to consider one or more test results where there is ambiguity orsuggested ambiguity as to the contributors and/or the genotypes of thecontributors. The method may be used to consider one or more testresults to which there is only one contributor and/or for which thegenotype is known.

A DNA based link may be present where the support that a genotype couldgive rise to the test result meets criteria for each of the test resultsfor which a link is determined. The criteria may be a predeterminedsupport level. The defined criteria may be a genotype whose support forgiving rise to the test results in the combination is above a definedlevel. The level may be predefined.

A DNA based link may be used to suggest or confirm a link between one ormore situations. The link may support other links for those situationsbased on other evidence types. The link may suggest links for whichlinks had not previously been suggested. The link may be used to directsubsequent investigation of the situations and/or events which gave riseto those situations and/or individuals behind those situations by lawenforcement agencies. The DNA based link may be used as evidence inlegal proceedings.

A genotype which is considered as a DNA based link between thesituations of the combination may be used in a further consideration.The further consideration may include the review of possible matchesbetween the genotype and a collection of genotype records. The existenceof a match may be deemed to occur where correspondence at or above agiven level of correspondence occurs. The given level may be at least80%, and ideally at least 90%, of alleles in common between thegenotypes. The recorded genotypes may be genotypes of known individuals.The further consideration may link the genotype to an individual. Thefurther consideration may link the situations of the combination of testresults to an individual.

The test result may be obtained, or have been obtained, by PCR basedamplification of DNA collected from the situation. The test result maybe obtained, or have been obtained, by establishing allele identitiesfor one or more loci of the DNA. The peak area and/or peak height forthe alleles may be obtained. The test results may be obtained for use inthe method and/or may have previously been obtained for other purposes.The test results may be reused in the method after use in other analysisand/or consideration methods.

The situations may be test results for different scenes and/or differentsamples from the same or different scenes and/or replicates from thesame samples or from different samples. The situations may include testresults for one or more known individuals. The test results may relateto mixtures and/or single contributor cases. The test results may relateto complete and/or partial profiles.

The number of test results obtained may be more than 10, more than 100or even more than 1000. The information on the DNA may be the identityof one or more alleles at one or more loci. The identity and peak heightand/or peak area may be obtained.

The group of test results may be in a formal group or may be testresults stored in a variety of locations. The group of test results mayinclude one or more test results from the test results for aninvestigation and/or one or more test results from the test results foranother, (potentially at the time of combinations selection, unrelated)investigation and/or one or more test results from a centralised store,such as The National DNA Database. The group of test results may includeall available test results.

According to a fourth aspect of the invention we provide a method ofconsidering DNA based links between two or more situations, the methodincluding:

-   -   obtaining a first test result for a first situation, the first        test result including information on the DNA from the first        situation;    -   considering a genotype as possibly giving rise to the first test        result and evaluating the support that the genotype gave rise to        the first test result, repeating the evaluation of the support        for a plurality of other genotypes, generating a set of possible        genotypes based on the evaluation with respect to the first test        result;    -   obtaining a second test result for a second situation, the        second test result including information on the DNA from the        second situation;    -   considering a genotype as possibly giving rise to the second        test result and evaluating the support that this genotype gave        rise to the second test result, repeating the evaluation of the        support for a plurality of other genotypes, generating a set of        possible genotypes based on the evaluation with respect to the        second test result;    -   combining the set of possible genotypes for the first test        result and the set of possible genotypes for the second test        result, genotypes present in the first set and the second set        being given a higher ranking in the combined set than genotypes        not present in one or more of the sets;    -   considering one or more of the higher ranked genotypes in the        combined set as a DNA based link between the first situation and        the second situation.

The fourth aspect of the invention may include any of the features,options or possibilities set out elsewhere in this document.

Each possible genotype may be considered as giving rise to a testresult. One or more limits may be applied to the genotypes which areconsidered from amongst the full set of possible genotypes. The limitsmay be based on one or more rules as to genotypes which could notpractically give the result being considered. The same or differentgenotypes may be considered for the different test results. Different,but preferably the same rules may be used as limits in considering eachtest result.

The evaluation of the support may involve a determination of the mixtureproportions contributed by different individuals. The determination mayinvolve the comparison of the observed and expected peak height and/orpeak area results at one or more loci. The peak area expected may besubtracted from the peak area observed for a locus, squared, and thensummed with the values for the other loci to give a residual. Accountmay be taken of errors in mixture proportion and/or peak areadeterminations.

The evaluation of the support may be used to rank the set. Preferablythe evaluation of the support includes a least squares based evaluation.The lower the value of the residual a genotype has, the higher rankingit may be given in the ranked evaluation. Preferably the same evaluationis used for each genotype considered and/or for each test resultconsidered.

The evaluation may produce a list of possible genotypes for the firstand second test results. The list may be ranked. The set may be in theform of a list.

The set or ranked evaluation or evaluations may include a pre-determinednumber of genotypes. The number may be at least 200 or even at least400. The number may be less than 1000. The set or ranked evaluation mayinclude all genotypes with a support above a pre-determined threshold.

Preferably the genotypes included in a set or ranked evaluation areranked within that evaluation.

Preferably the combining of the set for the first test result and theset for the second test result includes, for genotypes present in thefirst set and in the second set, adding the support for that genotypefor the first set to the support for that genotype for the second set.The residual value for a genotype in the first set may be added to theresidual value for the same genotype in the second set. Preferably thecombining of the set or ranked evaluation for the first test result andthe set or ranked evaluation for the second test result includescombining the support for that genotype for the set or ranked evaluationit is present in with a dummy support for the set or ranked evaluationit is absent from. The dummy may be a pre-set support value. The dummymay be a multiple of the support of the least likely genotype in the setor ranked evaluation from which the genotype was absent. The multiple ispreferably greater than 1, such as 2.

Preferably the genotypes are ranked within the combined set or combinedevaluation. Preferably genotypes present in each of the sets or rankedevaluations receive a high ranking in the combined set or rankedevaluation. Preferably genotypes absent from one or more of the sets ofranked evaluations receive a low ranking in the combined set or rankedevaluation.

The first and second test results may be from situations which differ interms of the scene and/or the sample and/or the replicate in question.

The method may be applied to three, four or more test results.

The method may be applied to test results in existing records. Each pairof test results and/or triple of test results and/or quadruple of testresults and/or higher combinations could be considered according to themethod.

The method may be used to consider one or more test results which aremixtures. The method may be used to consider one or more test resultswhich contain low levels of DNA from one or more persons. The method maybe used to consider one or more test results where there is ambiguity orsuggested ambiguity as to the contributors and/or the genotypes of thecontributors. The method may be used to consider one or more testresults to which there is only one contributor and/or for which thegenotype is known.

A genotype which is considered as a DNA based link between thesituations may be used in a further consideration. The furtherconsideration may include the review of possible matches between thegenotype and a collection of genotype records. The existence of a matchmay be deemed to occur where correspondence at or above a given level ofcorrespondence occurs. The given level may be at least 80%, and ideallyat least 90%, of alleles in common between the genotypes. The recordedgenotypes may be genotypes of known individuals. The furtherconsideration may link the genotype to an individual. The furtherconsideration may link the situations of the combination of test resultsto an individual.

The test results may be obtained, or have been obtained, by PCR basedamplification of DNA collected from the situations. The test results maybe obtained, or have been obtained, by establishing allele identitiesfor one or more loci of the DNA. The peak area and/or peak height forthe alleles may be obtained. The test results may be obtained for use inthe method and/or may have previously been obtained for other purposes.The test results may be reused in the method after use in other analysisand/or consideration methods.

The situations may be test results for different scenes and/or differentsamples from the same or different scenes and/or replicates from thesame samples or from different samples. The situations may include testresults for one or more known individuals. The test results may relateto mixtures and/or single contributor cases. The test results may relateto complete and/or partial profiles.

The number of test results considered may be more than 10, more than 100or even more than 1000.

The number of test results for which sets of possible genotypes arecombined may be two, three, four, five or more.

A DNA based link may be used to suggest or confirm a link between one ormore situations. The link may support other links for those situationsbased on other evidence types. The link may suggest links for whichlinks had not previously been suggested. The link may be used to directsubsequent investigation of the situations and/or events which gave riseto those situations and/or individuals behind those situations by lawenforcement agencies. The DNA based link may be used as evidence inlegal proceedings.

The test results may be selected from a formal group of results or maybe test results stored in a variety of locations. The test results mayinclude one or more test results from the test results for aninvestigation and/or one or more test results from the test results foranother, (potentially at the time of combinations selection, unrelated)investigation and/or one or more test results from a centralised store,such as The National DNA Database. The method may be applied to allavailable test results.

Various embodiments of the invention will now be described, by way ofexample only.

The present invention is aimed at establishing links between DNA testresults obtained from a series of situations. In general the DNA will becollected and analysed using conventional techniques, such as PCR basedamplification and gel electrophoresis to identify the alleles occurringat various loci for the DNA.

The situations being considered could be multiple scenes from which DNAis collected and/or multiple samples of DNA from different parts of asingle scene and/or even multiple replicates of DNA from a single samplewhich are analysed and generate test results. The DNA test resultsconsidered could, in one or more cases, have arisen from samples takenfrom known persons in controlled circumstances, such as the genotypeprofiles stored on The National DNA Database (Registered Trade Mark).The aim is to establish whether there are any well supported genotypes(those offering a sufficiently high probability), given the variousseparate test results obtained, for a particular combination ofsituations.

Taking the example of a serial offender there may be scenes whichinclude DNA of that offender and scenes which do not, samples from agiven scene which include DNA of that offender and samples which do notand even replicates of a sample which include a report of the DNA ofthat offender and other replicates which do not, despite thosereplicates arising from the same sample. Furthermore some of the samplesmay be single contributor samples and others may be mixtures involvingDNA contributed from a plurality of individuals. Determining linksbetween such scenes and/or samples and/or replicates is not an easy taskon an effective timescale.

The present invention provides an intelligence tool in which a DNA testresult from a situation is considered in combination with one or moretest results from other situations. The tool seeks to establishgenotypes which are more supported to arise from the test results inthat particular combination of such situations and thereby provide a DNAbased link between those situations. Of course the tool can be used toestablish that there is no likely link between the test results in thatcombination and still provide some useful information. The combinationof test results considered may particularly include test samples fromtwo or more different scenes, but is useful even where the test resultsare from different samples at the same scene, and even for differentreplicates of the same sample. The tool can also consider test resultcombinations which include test results from different types ofsituation.

The technique can be used to compare test results having one or moredifferent timings, including: the test results from the analysis ofpresent situations, for instance, recently occurred events under activelaw enforcement agency consideration for which test results are newlyavailable; the test results from the analysis of past situations, forinstance, past events no longer under active consideration for whichtest results were generated at the time or have now been generated; thetest results from analysis of known situations, for instance testresults obtained from known persons under controlled circumstances (suchas those used to generate The National DNA Database.

The tool may be used to investigate speculated or informed links betweensituations, which links are arrived at through other processes, byindicating a high level of support for one or more genotypes linkingthose situations given the test results for them. The tool may be usedto investigate in a non-premeditated manner a body of test results fromsituations with a view to generating suggested links. The tool may thusgenerated suggested links between situations not previously consideredin conjunction with one another. The tool can also be used to suggestlinks between one or more situations associated with a crime or sceneand a stored test result, previously obtained from a known individual.

Two main embodiments of the invention are now described with similarintents behind the process they facilitate and the uses they can be putto. In each case the aim is to identify one or more genotypes which issupported given the particular combination of test results (referred toas a partition) and hence the situations behind them. This providesinformation on links between crimes, locations and the like. As afurther part of the process the genotypes identified in this way canthen be compared with the genotype for a known situation to identify anymatches between that genotype and one of the particular supportedgenotypes. A link between the set of scenes and a known individual canthus be obtained.

In a first technique there is a general consideration of the probabilityof a genotype given the combination of test results/partition, using aconsideration of the probability of the test results arising given aspecific genotype (from amongst the many possibilities for the genotype)and the probability of occurrence of that specific genotype, comparedwith a consideration of the overall probability of the test resultsarising given a specific genotype and the probability of that genotype,for all the possible genotypes. The consideration can be represented as${\Pr\left( G_{l} \middle| {D\ldots} \right)} = {\frac{\prod\limits_{ijk}\quad{{\Pr\left( D_{ijk} \middle| G_{l} \right)}{\Pr\left( G_{l} \right)}}}{\sum\limits_{i}\quad{\prod\limits_{ijk}\quad{{\Pr\left( D_{ijk} \middle| G_{l} \right)}{\Pr\left( G_{l} \right)}}}}{for}\quad{all}\quad{l.}}$where i represents the range of replicates, j the range of samples, kthe range of scenes and 1 the range of genotypes under consideration.

This general consideration can be applied to one or morecombinations/partitions of test results from amongst the test resultsavailable. Indeed all such combinations/partitions can be considered inobtaining suggestions as to those which are linked and/or the level ofsupport for the linking supported genotype. A combination of situationsor a partition is a pair, triplet, quadruplet or higher number of testresults each from a different situation (such as replicates and/orsamples and/or scenes). By considering each of the possiblecombinations/partitions an indication will be provided of thosecombinations/partitions which are linked by DNA reported in the testresult for each of the situations behind it, due to the high posteriorprobability obtained from the consideration. A very large number of thecombinations/partitions will of course not be linked.

The outcome is one or more supported genotypes, each of the supportedgenotypes being the link for one or more of the combinations/partitions.Thus a supported genotype X may be suggested as being involved in apartition consisting of test results from five particular scenes; aseparate but supported genotype Y may be suggested as involved in fourscenes and so on. This linking of situations, particularly betweenscenes can be of great use in its own right. For instance, it may allowother evidence from a number of scenes to be considered in combinationwhen previously there was no such suggestion of a link. The otherevidence in combination may lead to the solving of the crime.

Once the supported genotypes with a high posterior probability given thetest results for that combination of situations or partition areobtained these supported genotypes can be used in furtherconsiderations. For instance each of those supported genotypes can beconsidered against records of genotypes for matches or near matches(90%+of the alleles in common, for example) so as to link the supportedgenotype to other situations, for instance scenes, samples orreplicates. This information can be used to confirm other evidenceand/or to direct future enquiries and/or to open up new lines of enquirytoo. In particular a link to an individual may be produced.

As a substantial number of the possible genotypes cannot arise given thetest results, the consideration is limited down quite significantly fromhaving to consider all the approximately 10²¹ genotypes possible intotal. With the processing side performed by a computer operating thedefined consideration, the large amount of processing involved can berealistically performed.

The manner in which the probability of the specific genotype given thetest results is considered can be as simply or as sophisticatedlyconsidered as is desired. Obviously more sophisticated considerationscan give greater confidence and worth to any combinations of situationsor partitions for which links are suggested. Thus it is desirable toinclude within that probability consideration one or more functions ormodels which can account for one or more factors such as genotypedropout, Pr(G_(D)), allele dropout, Pr(A_(D)), stutter, Pr(S),preferential amplification, Pr(PA) and others. These issues can all havean effect on the test result from a situation compared with the actualgenotype behind the DNA in that situation. Accounting for them makes theconsideration of the extent of support for the supported genotype morerobust.

To this end models for one or more of these factors can be included. Anillustration of the way in which these factors can be modelled isprovided in “An investigation of the rigor of interpretation rules forSTRs derived from less than 100 pg of DNA.” Gill et al., ForensicScience International 112 (2000) 17-40. Models to account for laboratoryintroduced contamination, allele drop out and stutter in particular areprovided. The paper is concerned with accounting for such factors in theanalysis of a single test result, however, and is not concerned with thebetween result considerations involved in this invention. The models arenone the less useful in assisting. Other models can be used, however,and other factors can be modelled.

In a second technique a test result for a situation is obtained and issubmitted to an evaluation of the likelihood of a genotype arising giventhat test result. A heuristic approach is taken; the general aim beingto list more supported genotypes ranked by residual of Euclideandistance.

The evaluation may use a technique such the Pendulum™ technique detailedin Gill et al, Forensic Science International 91 (1998) 41-53 togenerate the starting information. That paper describes theconsideration of the relative contribution of different individuals to amixture of DNA, followed by a consideration of the likelihood of thepossible genotypes as having been behind the test result obtained. Thecontents of that paper and in particular the disclosure of the manner inwhich the proportions of a mixture and the ranking of likelihood isperformed is incorporated herein by reference. The technique involves,for a single test result, the consideration of a number of locisimultaneously when establishing the likely mixing proportions and thelikely genotypes, but is only concerned with the analysis of anindividual situation. No between situation/test consideration isinvolved.

Other techniques for detailing likely genotypes behind an individualtest result can be used in a similar way to provide the startinginformation.

In the preferred embodiment, the starting information is provided by thePendlum™ technique and the output of this evaluation is a list ofgenotypes which give the lowest residual value from the evaluation used.In effect the most supported genotypes are assumed to be those with thelowest residuals. These are ranked from the lowest residual up to a cutoff point, which could be a residual level, but is normally a number ofgenotypes (frequently 500). An output listing for the test result of asituation A is provided below in Table A; the Genotype designationletters and residual values are schematic illustrations only. TABLE ANumber in list Genotype Residual value  1 Genotype AA 1.002 × 10⁶  2Genotype GR 1.058 × 10⁶  3 Genotype LD 1.078 × 10⁶  4 Genotype HU 1.092× 10⁶ — — — 499 Genotype KW 2.002 × 10⁶ 500 Genotype LM 2.097 × 10⁶

By repeating the evaluation for another test result, test result B, afurther output listing is obtained, as set out in Table B. This outputlisting is the test result from another situation, such as a sampleobtained from another scene, a sample taken from a different part of thesame scene or the like. TABLE B Number in list Genotype Residual value 1 Genotype JE 1.011 × 10⁶  2 Genotype QP 1.023 × 10⁶  3 Genotype LW1.085 × 10⁶  4 Genotype AA 1.101 × 10⁶ — — — 499 Genotype AS 1.989 × 10⁶500 Genotype YR 2.001 × 10⁶

If the output listings are then added to one another in a prescribedmanner a combined output listing can be obtained. This listing thenprovides indications as to those, if any, genotypes which are possiblyinvolved in the situations behind both the test results.

The same concept applies even if a combination of more than twosituations is being considered.

In this embodiment the prescribed manner of adding the output listingsto give the combined output listing involves the following rules. Wherethe same genotype is present in each of the output listings consideredthen the residuals for that genotype in each of the output listings areadded together. Where a genotype is absent from an output listing, adummy residual for each output listing the genotype is absent from isprovided and the residuals for the output listings the genotypes ispresent in are added to that dummy residual. The dummy residual in thisembodiment, in each case, is the largest residual of that output listingthe genotype is absent from multiplied by a factor (two in theillustrated example). The genotype can alternatively by rejectedentirely. The combined output listing presents the genotypes in orderbased on the residual level they have.

Considering the output listings of tables A and B it turns out thatGenotype AA is present in both output listings, as is a Genotype DSwhich had position 206 in Table A and position 56 in Table B. None ofthe other genotypes were present in both output listings. The combinedoutput listings is represented in Table C. TABLE C Number in listGenotype Combined residual value  1 Genotype AA 2.103 × 10⁶  2 GenotypeDS 3.103 × 10⁶  3 Genotype GR 5.060 × 10⁶  4 Genotype LD 5.080 × 10⁶  5Genotype HU 5.094 × 10⁶  6 Genotype JE 5.205 × 10⁶  7 Genotype QP 5.217× 10⁶  8 Genotype LW 5.279 × 10⁶ — — — 995 Genotype KW 6.004 × 10⁶ 996Genotype LM 6.099 × 10⁶ 997 Genotype AS 6.183 × 10⁶ 998 Genotype YR6.195 × 10⁶

As can be seen the two supported genotypes which are consideredpossibilities in each of the two output listings stand out in thecombined output listing when compared with the other genotypes and theirresidual values. This accurately reflects the status of these supportedgenotypes as being more supported candidates from both output listingsand the test results behind them, given the respective test results.Genotype AA ranks higher than Genotype DS in view of its higher rankingin each of the output listings.

Whilst the technique is illustrated above in relation to the combiningof two output listings, which in turn represent two test results, thetechnique can be applied to a larger number of output listings and theirunderlying test results in the same manner.

In practice it is envisaged that the technique, in any of itsembodiments, could be applied to a database of existing test results.Each pair of test results, each triplet of test results, each quadrupletof test results and so on could be considered; and as a result thesituations behind them. In this way any links between situations can beconsidered and highlighted in the combined output listing, withoutspeculating on links or suggesting links for consideration first. Thisis useful in approaching a body of unsolved or unlinked situations witha view to generating fresh avenues for investigation.

The technique could also be employed when a new test result or series oftest results are obtained from a new situation, such as a new scene.These test results can be considered in the same way in all possiblecombinations of situations, or partitions, with the pre-existing testresults to see whether this situation is linked to another.

The technique can also be used to test speculative or implied linksbetween situations, such as scenes and/or samples there from, based onother information or evidence.

As well as applying the technique in this way it is possible to use alimited number of test results from a plurality of situations to producea list of supported genotypes given those test results. These likelygenotypes can then form the basis of further searches or investigations.A given supported genotype can be compared with records of genotypesdetermined or suggested for other situations, such as from othersamples, for other scenes or from the testing of individuals todetermine their genotype. A match gives a link between them. The searchcan include not only direct matches but also take into account the factthat not all the prior genotypes may be complete. A match, therefore,may be deemed to extend to genotypes where the two are close to oneanother, for instance where they share 20 or 21 out of the 22 allelesconsidered in the determination of a test result. Again the genotypelinks suggested can link a variety of situations, such as scenes and/orsamples and/or individuals and/or events in a useful and informativeway.

1. A method of considering DNA based links between two or moresituations, the method including: obtaining a plurality of test results,each test result relating to a situation, each test result includinginformation on the DNA from that situation, the plurality of testresults providing a group of test results; selecting a plurality of testresults from the group of test results, the plurality of results forminga combination of test results; considering a genotype as possibly givingrise to each of the test results of the combination, evaluating thesupport for that genotype giving rise to all of the test results of thecombination; considering the genotype as a DNA based link between thesituations for the test results in the combination if the support meetsdefined criteria.
 2. A method according to claim 1 in which the methodincludes the further step of comparing a genotype which is considered aDNA based link against records of genotypes to identify matchinggenotypes in the records.
 3. A method according to claim 1 or claim 2 inwhich the evaluation involves a direct evaluation of the support for agenotype giving the combination of test results or involves anevaluation of the support for a given genotype giving each of the testresults, the individual evaluations being combined to give the overallevaluation.
 4. A method according to any preceding claim in which thesupport meets the defined criteria when the probability that thegenotype could have given rise to the test results of the combination isabove a given level and/or when an expression of the support that thegenotype could have given rise to the test results of the combination isbelow a given level.
 5. A method according to any preceding claim inwhich the evaluation of the support for a genotype giving rise to thecombination of test results includes a consideration of the probabilityof the test results arising given that genotype and the probability ofoccurrence of that genotype.
 6. A method according to any precedingclaim in which the evaluation of the support for a genotype giving riseto the combination of test results is defined by${\Pr\left( G_{l} \middle| {D\ldots} \right)} = {\frac{\prod\limits_{ijk}\quad{{\Pr\left( D_{ijk} \middle| G_{l} \right)}{\Pr\left( G_{l} \right)}}}{\sum\limits_{i}\quad{\prod\limits_{ijk}\quad{{\Pr\left( D_{ijk} \middle| G_{l} \right)}{\Pr\left( G_{l} \right)}}}}{for}\quad{all}\quad{l.}}$where G₁ represents the particular genotype, D represents thecombination of test results, potentially including test results due tovarious scenes and/or samples from scenes and/or replicates of samplesfrom scenes, i represents the range of replicates, j the range ofsamples, k the range of scenes and l the range of genotypes underconsideration.
 7. A method according to any preceding claim in which oneor more limits are applied to the genotypes which are considered fromamongst the full set of possible genotypes, the limits being based onone or more rules as to genotypes which could not practically give oneor more of the results in the combination being considered.
 8. A methodaccording to any preceding claim in which the evaluation of the supportfor a genotype giving rise to the group of test results includes aconsideration of the effect of one or more of contamination of the testresults and/or allele drop out from the results and/or stutter in theresults and/or preferential amplification of the results.
 9. A methodaccording to any preceding claim in which a genotype which is consideredas a DNA based link between the situations of the combination is used ina further consideration, the further consideration including the reviewof possible matches between the genotype and a collection of genotyperecords.
 10. A method of considering DNA based links between two or moresituations, preferably according to claim 1, the method including:obtaining a first test result for a first situation, the first testresult including information on the DNA from the first situation;considering a genotype as possibly giving rise to the first test resultand evaluating the support that the genotype gave rise to the first testresult, repeating the evaluation of the support for a plurality of othergenotypes, generating a set of possible genotypes based on theevaluation with respect to the first test result; obtaining a secondtest result for a second situation, the second test result includinginformation on the DNA from the second situation; considering a genotypeas possibly giving rise to the second test result and evaluating thesupport that this genotype gave rise to the second test result,repeating the evaluation of the support for a plurality of othergenotypes, generating a set of possible genotypes based on theevaluation with respect to the second test result; combining the set ofpossible genotypes for the first test result and the set of possiblegenotypes for the second test result, genotypes present in the first setand the second set being given a higher ranking in the combined set thangenotypes not present in one or more of the sets; considering one ormore of the higher ranked genotypes in the combined set as a DNA basedlink between the first situation and the second situation.
 11. A methodaccording to claim 10 in which the evaluation of the support involves adetermination of the mixture proportions contributed by differentindividuals.
 12. A method according to claim 10 or claim 11 in which theevaluation of the support is used to rank the set.
 13. A methodaccording to any of claims 10 to 12 in which the evaluation produces alist of possible genotypes for the first and second test results.
 14. Amethod according to any of claims 10 to 13 in which the combining of theset for the first test result and the set for the second test resultincludes, for genotypes present in the first set and in the second set,adding the support for that genotype for the first set to the supportfor that genotype for the second set.
 15. A method according to any ofclaims 10 to 14 in which the combining of the set or ranked evaluationfor the first test result and the set or ranked evaluation for thesecond test result includes combining the support for that genotype forthe set or ranked evaluation it is present in with a dummy support forthe set or ranked evaluation it is absent from.
 16. A method accordingto any of claims 10 to 15 in which the genotypes are ranked within thecombined set or combined evaluation, genotypes present in each of thesets or ranked evaluations receiving a high ranking in the combined setor ranked evaluation and/or genotypes absent from one or more of thesets of ranked evaluations receiving a low ranking in the combined setor ranked evaluation.